The novel is about a lonely young man, Frederick Clegg, who works as a clerk in a city hall, and collects butterflies in his spare time. The first part of the novel tells the story from his point of view.
Clegg is obsessed with Miranda Grey, a middle-class art student at the Slade School of Fine Art. He admires her from a distance, but is unable to make any contact with her because of his nonexistent social skills. One day, he wins a large prize in the British football pools. This makes it possible for him to stop working and buy an isolated house in the countryside. He feels lonely, however, and wants to be with Miranda. Unable to make any normal contact, Clegg decides to add her to his "collection" of pretty, petrified objects, in the hope that if he keeps her captive long enough, she will grow to love him. After careful preparations, he kidnaps Miranda by drugging her with chloroform and locks her up in the cellar of his house. He is convinced that Miranda will start to love him after some time. However, when she wakes up, she confronts him with his actions. Clegg is embarrassed, and promises to let her go after a month. He promises to show her "every respect", pledging not to sexually molest her and to shower her with gifts and the comforts of home, on one condition: she can't leave the cellar.
Clegg rationalizes every step of his plan in cold, emotionless language; he seems truly incapable of relating to other human beings and sharing real intimacy with them. He takes great pains to appear normal, however, and is greatly offended at the suggestion that his motives are anything but reasonable and genuine.
The second part of the novel is narrated by Miranda in the form of fragments from a diary that she keeps during her captivity. Clegg scares her, and she does not understand him in the beginning. Miranda reminisces over her previous life throughout this section of the novel, and many of her diary entries are written either to her sister, or to a man named...